Mono-1-olefins (alpha olefins), including ethylene, can be polymerized with catalyst systems employing titanium, zirconium, vanadium, chromium or other metals impregnated on a variety of support materials, often in the presence of activators. These catalyst systems can be useful for both the homopolymerization of ethylene and copolymerization of ethylene with comonomers such as propylene, 1-butene, 1-hexene, or higher alpha olefins. Because of the importance in this process for preparing functional materials, there exists a need and a constant search to develop new olefin polymerization catalysts, catalyst activation processes, and methods of making and using catalysts that will provide enhanced catalytic activities, selectivities, or new polymeric materials tailored to specific end uses.
One type of transition metal-based catalyst system utilizes metallocene compounds, often contacted with an activator such as methyl aluminoxane (MAO) to form an oligomerization catalyst. However, in order to achieve the desired high oligomerization activities, large amounts of expensive methyl aluminoxane typically are necessary to form the active metallocene catalysts. This feature has been an impediment to the commercialization of metallocene catalyst systems. Therefore improvements in catalyst systems and in methods of making the catalyst are needed to afford the desired oligomerization activities at reasonable commercial costs. Moreover, there remain important challenges in developing catalysts that can provide polymers or oligomers with the desired properties that can be tailored or maintained within a desired specification range.